South African Class 18 2-10-2

The South African Class 18 2-10-2 of 1927 is a South African steam locomotive from the South African Railways era.

In December 1927 and January 1928 the South African Railways placed two Class 18 steam locomotives with a 2-10-2 Santa Fe type wheel arrangement in service.^[1][3]

Manufacturer

The Class 18 2-10-2 Santa Fe type steam locomotive was designed by Colonel F.R. Collins, Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1922 to 1929, and built by Henschel and Son in Germany who delivered two locomotives in 1927 and 1928, numbered 1360 and 1361. They were very powerful three-cylinder locomotives, with their two outer cylinders using Walschaerts valve gear and the inner cylinder using Gresley conjugated valve gear that was actuated by the motions of the outer cylinders.^[1][4][5]

When delivered, the third cylinder was clearly visible, but plating that was subsequently added beneath the smokebox hid it from view. These were the most powerful non-articulated locomotives to see service on the SAR, with a tractive effort of no less than 53,650 pounds-force (238.647 kilonewtons) at 75% boiler pressure and capable of hauling loads of 1,800 long tons (1,828.9 tonnes) over the ruling gradient of 1 in 100 on the Witbank-Apex section.^[1][6]

Contemporary Henschel publicity appropriately referred to them as the "Henschel Giants". They were larger in most respects than Deutsche Reichsbahn’s new Standard gauge Class 44 three cylinder 2-10-0 locomotives. Although their all-up locomotive weight was almost the same, when considering the fact that the SAR’s Cape gauge Class 18 had shorter axles and frame strethers, saving weight that could then be built into other items such as the firebox, the Class 18 was the larger locomotive.^[5]

Characteristics

The Class 18 had a round top firebox with a combustion chamber, with arch tubes supporting the brick arch.^[5]

In order to allow the locomotive to negotiate curves of 320 feet (97.536 metres) radius despite its long coupled wheelbase, the third and fourth pairs of driving wheels were flangeless. In addition, the locomotive made use of a Krauss-Helmholtz bogie system, where the leading pair of driving wheels has a limited amount of sideplay with an articulated link to the leading bissel bogie. The bissel bogie was connected to a sleeve around the first driving axle so that any displacement of the bissel bogie in one direction would cause a similar displacement of the leading driving axle in the opposite direction, thereby steering the driving wheels through curves.^[1][4]

The outside cylinders drove the third pair of driving wheels while the inside cylinder drove the second pair through a cranked axle, with the cylinder mounted in an inclined position. The three cranks were arranged at an angle of 120 degrees to each other, allowing for the inclination of the inner cylinder.^[1][3]

Service

The Class 18 was introduced in an attempt to ease problems that were being experienced with increasingly heavy coal trains on the line between Witbank and Germiston, where the Class MF Mallets were considered as being too sluggish and the hauling capacity of the non-articulated fleet was being stretched to the limit of their capacity.^[1][4]

In spite of the two sets of flangeless driving wheels and the Krauss-Helmholtz system, the Class 18 experienced excessive flange and tyre wear. In addition, the complicated valve gear was not robust enough and required high maintenance, frequently giving trouble owing to wear and breakage. The result was that the locomotives had to be shopped at under 40,000 miles (64,374 kilometres). Both Class 18 locomotives were retired by 1951.^[1][4]

Features illustrated

The main picture and the following illustrate the Class 18 locomotive, one with the third cylinder exposed and another with the third cylinder hidden by plating beneath the smokebox. The construction of the Henschel Giant is shown in a cutaway diagram.

• 

  Class 18 with the third cylinder visible, as delivered, c. 1930

• 

  Cutaway diagram of a Class 18 2-10-2 locomotive

• 

  Class 18 at Germiston Loco with plating beneath the smokebox hiding the third cylinder

See also

• List of South African locomotive classes
• South African locomotive history
• Tender locomotive numbering and classification
• The 2-10-2 "Santa Fe"

References

Wikimedia Commons has media related to: South African Class 18 (2-10-2)

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